Vehicle tire

ABSTRACT

The invention relates in particular to a tire for a two-wheeled motorized vehicle and more particularly a motorcycle. Such a tire comprises a continuous carcass-type reinforcement structure, formed of reinforcement elements and anchored on each side of the tire to a bead whose base is intended to be fitted on a rim seat, each bead being extended radially towards the outside by a sidewall, the sidewalls meeting up radially towards the outside with a tread, and comprising under the tread a crown reinforcement structure consisting of at least one layer of reinforcement elements known as a working layer. According to the invention, said crown reinforcement structure does not comprise any circumferentially oriented reinforcement elements and, over the profile of the tire in a radial plane, in its part radially to the outside of the two points of tangency of the curvilinear abscissa of the carcass-type reinforcement structure with perpendiculars to the axis of rotation at least one layer of working reinforcement elements is at least partially radially to the inside of the part of the carcass-type reinforcement structure radially to the outside of the two points of tangency of the curvilinear abscissa of the carcass-type reinforcement structure with perpendiculars to the axis of rotation.

The present invention relates to a tire intended to be fitted on avehicle and more particularly intended to be fitted on a two-wheeledvehicle such as a motorcycle.

Although not limited to such an application, the invention will be moreparticularly described with reference to such a motorcycle, ormotorbike, tire.

Tire reinforcement armatures or tire reinforcements, in particular formotorcycle tires, are currently—and most frequently—formed by stackingone or more plies conventionally designated “carcass plies”, “crownplies”, etc. This way of designating reinforcement armatures stems fromthe manufacturing process, which consists of making a series ofsemi-finished products in the form of plies, provided with, oftenlongitudinal, cord reinforcements, which are then assembled or stackedso as to build a tire blank. The plies are made flat, with largedimensions, and are then cut as a function of the dimensions of a givenproduct. The plies are also assembled substantially flat in a firstphase. The blank thus produced is then shaped into the toroidal profiletypical of tires. The semi-finished products known as “finishingproducts” are then applied to the blank, in order to obtain a productwhich is ready for vulcanization.

Such a “conventional” type of process involves, in particular for thetire blank manufacturing phase, the use of an anchoring element(generally a bead wire), used to effect anchoring or retention of thecarcass reinforcement in the tire bead zone. Thus, for this type ofprocess, a turn-up is formed from a portion of all the pliesconstituting the carcass reinforcement (or of only some) around a beadwire disposed in the bead of the tire. The carcass reinforcement isthereby anchored in the bead.

The widespread use in the industry of this type of conventional process,despite numerous variants in the manner of producing the plies and theassemblies, has led the person skilled in the art to use a vocabularyderived from the process; hence the terminology in general use,comprising in particular the terms “plies”, “carcass”, “bead wire”,“shaping” to designate transition from a flat profile to a toroidalprofile, etc.

Tires now exist which do not strictly speaking comprise “plies” or “beadwires” which fit the above definitions. For example, document EP 0 582196 describes tires manufactured without the aid of semi-finishedproducts in the form of plies. For example, the reinforcement elementsof the various reinforcement structures are applied directly onto theadjacent layers of rubber mixes, the whole being applied in successivelayers onto a toroidal core whose shape allows the direct obtainment ofa profile resembling the final profile of the tire in the process ofbeing manufactured. Thus, in this case there are no longer“semi-finished products”, or “plies” or “bead wires”. The basic productssuch as the rubber mixes and the reinforcement elements in the form ofcords or filaments are applied directly to the core. Since this core istoroidal in shape, the blank no longer has to be shaped in order to betransformed from a flat profile to a profile in the form of a torus.

Furthermore, the tires described in this document do not have the“traditional” carcass ply turn-up about a bead wire. This type ofanchoring is replaced by an arrangement in which circumferential cordsare disposed adjacent to said sidewall reinforcing structure, the wholebeing immersed in an anchoring or bonding rubber mix.

Assembling processes using a toroidal core also exist which usesemi-finished products specially adapted for rapid, effective and simplelaying on a central core. Finally, it is also possible to use acomposite comprising certain semi-finished products to achieve certainarchitectural aspects (such as plies, bead wires, etc), while others areachieved by the direct application of mixes and/or reinforcementelements.

In the present document, so as to take account of recent technologicaldevelopments both in the field of manufacture and in the design ofproducts, the conventional terms such as “plies”, “bead wires” etc areadvantageously replaced by neutral terms or terms which are independentof the type of process used. Thus, the term “reinforcement of carcasstype” or “sidewall reinforcement” may be used to denote thereinforcement elements of a carcass ply in the conventional process andthe corresponding reinforcement elements, generally applied at the levelof the sidewalls, of a tire produced according to a process not usingsemi-finished products. The term “anchoring zone”, for its part, maydenote both the “traditional” carcass ply turn-up about a bead wire of aconventional process and the assembly formed by the circumferentialreinforcement elements, the rubber mix and the adjacent sidewallreinforcement portions of a bottom zone produced using a processinvolving application on a toroidal core.

As in the case of all other tires, we are witnessing the radializationof motorcycle tires, the architecture of such tires comprising a carcassreinforcement formed of one or two layers of reinforcement elementsforming with the circumferential direction an angle which may be between65° and 90°, said carcass reinforcement being radially surmounted by acrown reinforcement formed at least of generally textile reinforcementelements. Non-radial tires do still exist, however, and the inventionalso relates to them. The invention also relates to partially radialtires, that is to say whose reinforcement elements of the carcassreinforcement are radial over at least part of said carcassreinforcement, for example in the part corresponding to the crown of thetire.

Numerous crown reinforcement architectures have been proposed, dependingon whether the tire is intended to be fitted at the front of themotorcycle or at the rear. A first structure consists, for said crownreinforcement, in using solely circumferential cables, and saidstructure is more particularly used for the rear position. A secondstructure, directly inspired by structures commonly used inpassenger-vehicle tires, has been used to improve wear resistance, andconsists in using at least two crown layers of reinforcement elementswhich are parallel to each other within each layer but crossed from onelayer to the next, forming acute angles with the circumferentialdirection, such tires being more particularly suitable for the front ofmotorcycles. Said two crown layers may be associated with at least onelayer of circumferential elements, generally obtained by helical windingof a strip of at least one reinforcement element coated with rubber.

Patent no. FR 2 561 588 thus describes such a crown reinforcement,having at least one ply whose reinforcement elements form with thecircumferential direction an angle which may vary between 0° and 8°, themodulus of elasticity of such elements amounting to at least 6000 N/mm²,and, disposed between the carcass reinforcement and the ply ofcircumferential elements, a shock-absorption layer formed mainly of twoplies of elements crossed from one ply to the next forming between themangles of between 600 and 90°, said crossed plies being formed oftextile reinforcement elements having a modulus of elasticity of atleast 6000 N/mm².

Document EP 0 456 933, with a view to providing a motorcycle tire withexcellent stability at high speed as well as excellent contact with theground, teaches for example that a crown reinforcement should be madewith at least two plies: a first ply, radially the closest to thecarcass reinforcement, being composed of cables oriented at an angle ofbetween 40° and 90° relative to the circumferential direction and thesecond ply, radially the closest to the tread, being composed of cableswound helically in the circumferential direction.

U.S. Pat. No. 5,301,730, with a view to enhancing the drive ability of atire designed for the rear of a motorcycle, proposes a crownreinforcement composed, proceeding from the radial carcass reinforcementto the tread, of at least one ply of substantially circumferentialelements and two plies of elements crossed from one ply to the next andforming with the circumferential direction an angle which may be between35° and 55°, elements of aromatic polyamide being suitable for use asthe ply of elements parallel to the circumferential direction andaliphatic polyamide being suitable for the plies of crossed elements.

The object of the invention is to provide motorcycle tires whose crownreinforcement structure does not comprise any circumferentially orientedreinforcement elements and comprises at least one layer of workingreinforcement elements, at lower cost than those currently obtained,without for all that impairing the properties required to satisfy theusers.

This aim is achieved according to the invention by a tire comprising acontinuous carcass-type reinforcement structure, formed of reinforcementelements and anchored on each side of the tire to a bead whose base isintended to be fitted on a rim seat, each bead being extended radiallytowards the outside by a sidewall, the sidewalls meeting up radiallytowards the outside with a tread, and comprising under the tread a crownreinforcement structure consisting of at least one at least one layer ofreinforcement elements known as a working layer, said crownreinforcement structure not comprising any circumferentially orientedreinforcement elements, and, over the profile of the tire in a radialplane, in its part radially to the outside of the two points of tangencyof the curvilinear abscissa of the carcass-type reinforcement structurewith perpendiculars to the axis of rotation at least one layer ofworking reinforcement elements being at least partially radially to theinside of the part of the carcass-type reinforcement structure radiallyto the outside of the two points of tangency of the curvilinear abscissaof said carcass-type reinforcement structure with perpendiculars to theaxis of rotation.

The longitudinal direction of the tire, or circumferential direction, isthe direction corresponding to the periphery of the tire and defined bythe rolling direction of the tire.

A circumferential plane or circumferential section plane is a planeperpendicular to the axis of rotation of the tire. The equatorial planeis the circumferential plane passing through the centre or crown of thetread.

The transverse or axial direction of the tire is parallel to the axis ofrotation of the tire.

A radial plane contains the axis of rotation of the tire.

For the purposes of the present invention, a working ply has acurvilinear abscissa between the two points of tangency of thecurvilinear abscissa of the carcass-type reinforcement structure withperpendiculars to the axis of rotation; the axial width of a working plyis thus less than the axial distance between these two points oftangency of the curvilinear abscissa of the carcass-type reinforcementstructure with perpendiculars to the axis of rotation.

For the purposes of the invention, a continuous carcass-typereinforcement structure is formed of reinforcement elements which arecontinuous from one bead to the other.

The tire according to the invention allows financial savings on twocounts. Firstly, the quantity of material used to form a layer ofworking reinforcement elements is reduced relative to a conventionaltire of the same dimensions, due to the radially inner position of atleast part of a layer of working reinforcement elements relative to thecarcass-type reinforcing structure. Consequently, the manufacturing timefor said layer of working reinforcement elements may be less than thatnecessary to produce the layer of a conventional tire, in particular inthe case of production using a hard core.

According to the invention, when the tire comprises at least twocarcass-type reinforcement layers, at least one layer of workingreinforcement elements is positioned at least in part radially to theinside of at least two carcass-type reinforcement layers.

A tire according to the invention, having at least one part of the crownreinforcement structure formed radially to the inside of thecarcass-type reinforcement structure, is thus advantageously producedusing a manufacturing method of the hard core or rigid form type.

According to a first embodiment of the invention, the crownreinforcement structure is entirely produced radially to the inside ofat least one carcass structure, that is to say to the inside of at leastone carcass layer. At least one carcass-type reinforcement structurethus radially covers the entire crown reinforcement structure.

According to a second preferred embodiment of the invention, at leastone layer of working reinforcement elements of the crown reinforcementstructure is provided radially to the outside of the carcass-typereinforcement structure. According to this second embodiment of theinvention, the layer of working reinforcement elements assumes thefunction of protecting the carcass and the other layers of the crownreinforcement structure against possible mechanical stresses.

In an advantageous variant of the invention, a layer of workingreinforcement elements may be provided in several parts positioned atvarious radial positions or different levels of the tire. Such a tiremay in particular comprise a part of the layer of working reinforcementelements radially to the outside of the reinforcement elements of thecarcass structure in the central part of the tire, that is to say underthe central part of the tread. This part of the layer of workingreinforcement elements thus allows in particular protection of thecarcass against any stresses which may affect the central part of thetread, considered as the most exposed. The invention additionallyprovides, in the case of a layer of working reinforcement elements madein several parts positioned in different radial positions, for thedistribution of these various parts not to be symmetrical relative tothe equatorial plane, or circumferential plane passing through thecentre of the crown of the tire. Such an asymmetrical distribution mayadditionally be associated with the selection of different materials forthe reinforcement elements of the working layers.

In accordance with this type of embodiment of a layer of workingreinforcement elements divided into several parts, the inventionadvantageously provides mutual overlapping of the axial ends of saidparts.

According to an advantageous variant of the invention, at least onelayer of working reinforcement elements consists of at least onecontinuous reinforcement cord forming in the central zone of said layerportions having identical angles formed with the longitudinal direction,said angles being measured at the points of intersection with acircumferential plane, two adjacent portions being linked by a loop orbend formed by said cord, and the portions forming an angle with thelongitudinal direction of between 10 and 80°.

According to a preferred embodiment of the invention, in the centralzone of said working layer the portions are equidistant from one anotherover all circumferential planes.

Other advantageous embodiments of the invention additionally provide forthe portion patterns to be equidistant from one another over allcircumferential planes. Portion pattern should be understood to mean anassembly of several portions disposed in a given, repeatedconfiguration.

The central zone of a working layer is a circumferential zone of saidlayer axially between two lateral zones, axially outside said centralzone. According to a preferred embodiment of the invention, this centralzone is centered on the crown of the tire tread.

The term “cord” generally denotes any of monofilaments, multifilamentfibers (possibly twisted around themselves) or assemblies such astextile or metal cables, plied yarn or alternatively any type ofequivalent assembly such as, for example, a hybrid cable, this being thecase whatever the material(s) or the possible treatment of these cords,for example surface treatment or coating or pre-sizing to improveadhesion to the rubber or any other material.

According to this advantageous variant of the invention, the workinglayer is made with at least one cord, of which no free end is present atthe edges of said layer. Preferably, the layer is made with a singlecord and the layer is of the “mono-filament” type. However, industrialproduction of such layers results in discontinuities, in particular dueto reel changes. A preferred embodiment of the invention furtherconsists in using only a single or a small number of cords for a workinglayer and it is appropriate to arrange the beginnings and ends of cordsin the central zone of said layer.

A tire produced thus according to the invention comprises areinforcement structure which does not exhibit any reinforcement elementfree end at the level of the axially outer edges of the working layers.

Studies carried out have shown in particular that the presence ofconventional layers of reinforcement elements forming an angle with thelongitudinal direction results in local circumferential and shearingrigidities which diminish near the edges of said layers, the tension atthe ends of the reinforcement elements being zero. A local tension ofzero for the reinforcement elements results in reduced effectiveness ofsaid reinforcement elements in this zone. The rigidities of the edges ofthe layers are particularly important when the tire is used on the mostsevere cambers, when cornering, the part of the tire corresponding tosaid zones then facing the ground.

The production of motorcycle tires results in large curvature values ifsuch tires are to be used on a camber. A tire produced according to thisvariant of the invention and which comprises a reinforcement structurewhich does not exhibit any reinforcement element free end at the levelof the axially outer edges of the working layers thus makes it possiblein particular to consolidate the properties of tire grip and driveability for use on severe camber.

In the central zone of the working layers, that is to say in the part ofthe working layers which does not include the loops linking the portionstogether, the portions display identical angles formed with thelongitudinal direction, said angles being measured at the points ofintersection with a circumferential plane, whatever is saidcircumferential plane. In other words, for a given circumferentialsection plane, the portions all display the same angle formed with thelongitudinal direction at the points of intersection with saidcircumferential section plane. Furthermore, the above-mentioned anglemay vary depending on the circumferential section plane considered.

According to a previously mentioned preferred embodiment, in the centralzone of the working layers the portions are equidistant from one anotherin circumferential section planes; the distance between adjacentportions being able itself to vary depending on the circumferentialsection plane considered, or more precisely, the distance betweenadjacent portions being capable of varying in the axial direction.

Such a tire which, as mentioned above, is advantageously made using amethod of the hard or toroidal core type, allows in particularpositioning of the reinforcement elements in the quasi-final position;in fact, since a shaping stage is not required with this type ofprocess, the reinforcement elements are not displaced any more aftertheir positioning. If a method comprising a shaping stage, such asshaping or application of a flat ply on the profile of the tire, isused, the curvature of a motorcycle tire necessitates preparation of aspecial ply for allowing the obtainment of portions, displayingidentical angles and possibly equidistant from one another over allcircumferential planes, linked by a loop; in particular at the ends ofthe ply and therefore at the level of the loops, shaping in accordancewith the curvature of a motorcycle tire results in variations inparticular at the edges of the tire which modify the position of thereinforcement elements. This modification of the positions isadditionally disrupted by the presence of the loops, which causenon-homogeneous modifications. For this reason, the various portions donot display angles, formed with the longitudinal direction, which areidentical in the circumferential section planes. Likewise, they are notequidistant from one another in circumferential section planes.

In an advantageous embodiment of the invention, in particular in orderto optimize the rigidities of the reinforcement structure along themeridian of the tire, and in particular at the edges of the workinglayers, the angles formed by said portions of the cord of the workinglayers with the longitudinal direction are variable in the transversedirection such that said angles are greater at the axially outer edgesof the layers of reinforcement elements relative to the angles of saidportions measured at the level of the equatorial plane of the tire.

Use of a method of the hard core type which in particular allowspositioning of the reinforcement elements in the quasi-final positionwithout the need for a shaping stage exhibits further advantages. Infact, a method of the hard core type in particular allows simple anglevariations distinctly greater than it is possible to obtain usingprocesses comprising a shaping stage. Furthermore, said anglevariations, said angle tending towards 90° at the edges of the workinglayers, result in an increase in pitch and promote production of theloops, due to the reduction in bulk.

The invention further proposes a tire comprising a continuouscarcass-type reinforcement structure, formed of reinforcement elementsand anchored on each side of the tire to a bead whose base is intendedto be fitted on a rim seat, each bead being extended radially towardsthe outside by a sidewall, the sidewalls meeting up radially towards theoutside with a tread, and comprising under the tread a crownreinforcement structure consisting of at least one layer ofreinforcement elements known as a working layer and not comprising anycircumferentially oriented reinforcement elements, and, over the profileof the tire in a radial plane, at least one layer of workingreinforcement elements being at least partially radially to the insideof the part, of the carcass-type reinforcement structure, radially tothe outside of the two points of tangency of the curvilinear abscissa ofsaid carcass-type reinforcement structure with perpendiculars to theaxis of rotation, said layer of working reinforcement elementsconsisting of at least one continuous reinforcement cord forming in thecentral zone of said layer portions, such that two adjacent portions arelinked by a loop, and such that said portions form an angle with thelongitudinal direction of between 10 and 80°, said angles formed by saidportions with the longitudinal direction being variable in thetransverse direction in such a way that said angles are greater at theaxially outer edges of the layers of reinforcement elements relative tothe angles of said portions measured at the level of the equatorialplane of the tire.

A first embodiment of the variant embodiments of the invention accordingto which the angles formed by said portions of the cord of the workinglayers with the longitudinal direction are variable in the transversedirection consists in varying the angle of the portions in monotonicmanner from the equatorial plane of the tire as far as the edges of theworking layer.

A second embodiment of these variants consists in making the angledevelop by stages from the equatorial plane of the tire as far as theedges of the working layer.

A last embodiment of these variants consists in the angle developingsuch that given values are obtained for given axial positions.

These various embodiments of the variant embodiments of the inventionaccording to which the angles formed by said portions of the cord of theworking layers with the longitudinal direction are variable in thetransverse direction allow in other words the obtainment of considerablecircumferential rigidity of the crown reinforcement structure due to thepresence of closed, that is to say small, angles in the crown zone ofthe tire, that is to say in the zone surrounding the equatorial plane.And, on the other hand, the presence of open angles, that is to sayangles tending towards 45°, or even towards 90°, may be obtained at theedges of the working layer or more precisely at the level of theshoulders of the tire to improve the grip, drive ability, comfort, orindeed the operating temperature of the tire; in fact, such variationsin angle allow adjustment of the shearing rigidities of the workinglayers.

Advantageously, in the case of a radial structure, the reinforcementelements of the carcass-type reinforcement structure form an angle ofbetween 65° and 90° with the circumferential direction.

According to preferred embodiments of the invention, the portions forman angle with the longitudinal direction of between 20 and 75°.Preferably, the angle is less than 50° and more preferably less than40°.

According to a preferred embodiment of the invention, the crownreinforcement structure of the tire comprises at least two layers ofreinforcement elements such that from one layer to the next the portionsform between them angles of between 20 and 160° and preferably between40 and 100°.

According to a preferred embodiment of the invention, the reinforcementelements of the working layers are of textile material.

According to another embodiment of the invention, the reinforcementelements of the working layers are of metal.

Other advantageous details and features of the invention will becomeclear below from the description of examples of embodiment of theinvention made with reference to FIGS. 1 to 5, in which:

FIG. 1 is a meridian view of a diagram of a tire according to oneembodiment of the invention,

FIG. 2 a is a diagrammatic representation of a working layer accordingto a first embodiment of the invention,

FIG. 2 b is a diagrammatic representation of a working layer accordingto a second embodiment of the invention,

FIG. 3 is a meridian view of a diagram of a tire according to a secondembodiment of the invention,

FIG. 4 is a meridian view of a diagram of a tire according to a thirdembodiment of the invention,

FIG. 5 is a meridian view of a diagram of a tire according to a fourthembodiment of the invention.

To simplify understanding thereof, FIGS. 1 to 5 are not to scale.

FIG. 1 shows a tire 1 comprising a carcass reinforcement consisting of asingle layer 2 comprising reinforcement elements of textile type. Thelayer 2 consists of reinforcement elements disposed radially. The radialpositioning of the reinforcement elements is defined by the laying angleof said reinforcement elements; a radial arrangement corresponds to alaying angle of said elements relative to the longitudinal direction ofthe tire of between 65° and 90°.

Said carcass layer 2 is anchored on either side of the tire 1 in a bead3 whose base is intended to be mounted on a rim seat. Each bead 3 isextended radially towards the outside by a sidewall 4, said sidewall 4meeting up radially towards the outside with the tread 5. The tire 1thus constituted has a value of curvature greater than 0.15 andpreferably greater than 0.3. The value of curvature is defined by theHt/Wt ratio, that is to say by the ratio of the height of the tread tothe maximum width of the tread of the tire. The value of curvature willadvantageously be between 0.25 and 0.5 for a tire intended to be fittedat the front of a motorcycle and it will advantageously be between 0.2and 0.5 for a tire intended to be fitted at the rear.

The tire 1 further comprises under the tread a crown reinforcementconsisting in the present case of two working layers 6, 7. Said workinglayers 6, 7 are, in accordance with the invention, positioned radiallyto the inside of the part of the carcass layer 2 radially outside thetwo points of tangency A, B of the curvilinear abscissa of said carcasslayer 2 with the perpendiculars 100, 101 to the axis of rotation.

As mentioned above, an embodiment of this type allows financial savingson two counts. Firstly, the quantity of material used to form suchlayers of working reinforcement elements is reduced due to the radialposition of the layers 6 and 7 to the inside of the carcass layer 2compared with the same tire produced in conventional manner with workinglayers radially outside the carcass. And consequently, the laying timefor the reinforcement cord of said layers 6 and 7 is also less than thetime necessary for production of the above-mentioned conventionallayers.

The working layers 6, 7 consist of textile reinforcements producedaccording to the invention with at least one continuous reinforcing cordforming parallel portions in the central zone of said layer and theadjacent portions being connected by loops. The arrangement of the cordsis such that the portions are crossed from a layer 6 to the followinglayer 7.

FIG. 2 a illustrates an example of embodiment according to the inventionof such a working layer 6 consisting of a single cord 9 positioned toform portions 10. Two adjacent portions are connected by loops 11. Theportions 10 are so oriented that they form with the longitudinaldirection L an angle of between 10 and 80°. In this illustration in FIG.2, the portions are formed with an angle which may vary in such a waythat, at the edges of the working layer 6, said angle becomes larger.Such a variant embodiment in particular allows considerablecircumferential rigidity to be imparted around the equator, that is tosay in the central part of the tire where the angles of said portionsare smallest so as to resist centrifugation. On the other hand, thelargest angles at the edge of the working layer 6 and advantageously atthe level of the shoulders allow improvement of the grip and driveability of the tire at a camber by optimizing the shearing rigidity ofthe working layers when the angle is around 45° or alternativelyimprovement of comfort at a camber when the angle approaches 90°.

FIG. 2 a also shows two circumferential section planes XX′ and YY′ andthe angles α and β formed by the reinforcement elements with thelongitudinal direction at the various points of intersection with saidcircumferential planes XX′ and YY′. The angles α on the one hand and βon the other hand are identical whichever reinforcement element isconsidered. Furthermore, the angles α and β are different one from theother.

FIG. 2 a also shows that, when the layer 6 is centered on the crown orequator of the tire, the equator forms a line 12 comprising theinflection points of the portions 10 formed by the cord 9.

FIG. 2 b illustrates another variant embodiment of the invention similarto that of FIG. 2 a according to which the length of the portions is notregular. In the case of FIG. 2 b, the cord 9′ is deposited so as to formportions 10′, 10″ of two different lengths. Such a configuration allowsthe obtainment of variations in density in the axial direction, thequantity of reinforcement elements varying in this same direction.Variations in density of this type are all the more significant indesigning tires for motorcycles with regard to optimizing and adaptingthe different rigidities of the working layers required between thestraight line positions and the various inclined positions of the tiredue to the different parts of the tread and of the reinforcementstructure which face the ground.

In the case of FIG. 2 b, two different portion lengths are provided, butthe invention must not be interpreted as limited to this scenario, itbeing possible for the number of different portion lengths to begreater.

According to one or other of the embodiments illustrated in FIGS. 2 aand 2 b, the layers 6 and 6′ are preferably made with a single cord.However, for various reasons, deliberate or otherwise, in the case whereseveral cords are used to produce a working layer 6, 7, 6′, 7′, the endsof said cords are located in the central part of the tire. Moreprecisely, no free end appears at the edges of the working layers; allthat is present at this level of the working layers is the loops 11,11′. This feature of the invention, according to which no reinforcementelement free end is present at the working layer edges makes it possibleto improve the quality and more particularly the grip, drive ability,comfort, or indeed operating temperature of the tires without impairingthe various desired properties associated with the production of saidtires.

Furthermore, with regard to the production of such a tire, this isadvantageously obtained by manufacture of the hard core type. Thus,laying of the cords 9, 9′ may be performed by a robot which depositsthem precisely at the desired angles in their quasi-final position. Infact, hard core type manufacture allows precise positioning of the cordsbecause, since the hard core sets the required internal cavity shape,the profile of the tire is not subject to modification during building.

FIG. 3 shows a tire 13 which is a variant embodiment of FIG. 1.According to this variant embodiment, the working layer 63 is formedradially to the inside of the carcass layer 2 radially covered by theworking layer 73. The working layer 73 then has, in addition to itsprimary function, a protective function, in particular providingprotection for the carcass layer 2.

FIG. 4 shows an embodiment of the invention according to which theworking layer 64 is formed of several parts 64 a, 64 b, 64 c positionedon the tire 14 at radially different levels. Such embodiments, forexample, allow the working layer 64 locally to maintain a protectiverole in particular with regard to the carcass ply 24 and furthermoreallow manufacturing costs to be reduced by forming said working layer 64in part in radially lower positions. This choice may also influenceother properties of the tire which are only required locally. In thecase shown in FIG. 4, the position of the axially outer parts 64 b, 64 cradially to the outside of the carcass layer 24 in particular allows animprovement in stability at a severe camber. The tire further comprisesa working layer 74 likewise fulfilling a protective function.

FIG. 5 shows, as in the case of FIG. 4, an embodiment of the inventionaccording to which the working layer 65 is provided in a number of parts65 a, 65 b, positioned on the tire 15 at radially different levels. Incontrast to FIG. 4, the representation in this FIG. 5 does not exhibitsymmetry relative to the equatorial plane 20. Such an embodiment may beparticularly sought after when use of the tire 15 will itself not besymmetrical; for example, in the case of tires designed for use onspecific circuits which subject the tire to camber stress alongsubstantially one side. In fact, the provision of such a tire may beparticularly relevant to use on a track where the majority of the curvesor bends are in the same direction.

Such an embodiment of the working layer 65 in several parts may also becombined with the presence of a second working layer 75 radially to theoutside of the carcass layer 25, in particular for reinforcing theprotective function with regard to the carcass layer 25.

1- A tire comprising a continuous carcass-type reinforcement structure,formed of reinforcement elements and anchored on each side of the tireto a bead whose base is intended to be fitted on a rim seat, each beadbeing extended radially towards the outside by a sidewall, the sidewallsmeeting up radially towards the outside with a tread, and comprisingunder the tread a crown reinforcement structure consisting of at leastone layer of reinforcement elements known as a working layer, said crownreinforcement structure not comprising any circumferentially orientedreinforcement elements, wherein, over the profile of the tire in aradial plane, in its part radially to the outside of the two points oftangency of the curvilinear abscissa of the carcass-type reinforcementstructure with perpendiculars to the axis of rotation at least one layerof working reinforcement elements is at least partially radially to theinside of the part of the carcass-type reinforcement structure radiallyto the outside of the two points of tangency of the curvilinear abscissaof the carcass-type reinforcement structure with perpendiculars to theaxis of rotation. 2- A tire according to claim 1, wherein at least onelayer of working reinforcement elements consists of at least onecontinuous reinforcement cord forming in the central zone of said layerportions having identical angles formed with the longitudinal direction,said angles being measured at the points of intersection with acircumferential plane, wherein two adjacent portions are linked by aloop, and wherein the portions form an angle with the longitudinaldirection of between 10 and 80°. 3- A tire according to claim 2,wherein, in the central zone of said layer, the portions are equidistantfrom one another over all circumferential planes. 4- A tire according toclaim 2, wherein the angles formed by said portions with thelongitudinal direction are variable in the transverse direction andwherein said angles are greater at the axially outer edges of the layersof reinforcement elements relative to the angles of said portionsmeasured at the level of the equatorial plane of the tire. 5- A tireaccording to claim 1, wherein at least one layer of workingreinforcement elements consists of at least one continuous reinforcementcord forming portions in the central zone of said layer, wherein twoadjacent portions are linked by a loop, wherein said portions form anangle with the longitudinal direction of between 10 and 80°, wherein theangles formed by said portions with the longitudinal direction arevariable in the transverse direction and wherein said angles are greaterat the axially outer edges of the layers of reinforcement elementsrelative to the angles of said portions measured at the level of theequatorial plane of the tire. 6- A tire according to claim 4 or 5,wherein the angles of the portions vary in monotonic manner from theequatorial plane of the tire as far as the edges of the working layer.7- A tire according to claim 4 or 5, wherein the angles of the portionsvary by stages from the equatorial plane of the tire as far as the edgesof the working layer. 8- A tire according to claim 1, wherein the crownreinforcement structure comprises at least two layers of reinforcementelements and wherein from one layer to the next the portions formbetween them angles of between 20 and 160°. 9- A tire according to claim1, wherein the reinforcement elements of the carcass-type reinforcementstructure form an angle of between 65° and 90° with the circumferentialdirection. 10- A tire according to claim 1, wherein the working layerreinforcement elements are of textile material. 11- A tire according toclaim 1, wherein the working layer reinforcement elements are of metal.